The increasing demand for electrical power has forced electrical utilities to bum increasing quantities of fossil fuels such as coal and oil. However, electric utilities also face increasing environmental standards imposed upon their operations by state and federal regulatory agencies that mandate reduced particulate and acid generating smoke stack emissions. To reduce acid generating emissions, electrical utilities have turned to burning low-sulfur coal in their boilers to generate the steam necessary for electric power generation. To reduce the particulate emissions, electric utilities generally use a flue gas treatment system to remove a majority of the particulate matter in the gas effluent passing out of the smoke stack. Such flue gas treatment systems typically comprise an electrostatic device such as an electrostatic precipitator or a fabric filter baghouse to remove the particulate. Such devices may also provide a source of conditioning agent to the flue gas to enhance the effectiveness of the precipitator or filter in removing the particulate.
The efficiency of an electrostatic precipitator in removing particulate matter from the boiler flue gas is partially dependent upon the electrical resistivity of the entrained particulate matter in the boiler flue gas. The entrained particulate matter expelled from a boiler fired with low-sulfur coal, i.e., coal having less than 1 percent sulfur, has been found to have a resistivity of approximately 10.sup.13 ohms/cm. It has been determined that the most efficient removal of particulate matter by electrostatic precipitation occurs when the particulate matter resistivity is approximately 10.sup.10 ohms/cm. Therefore, to obtain more effective use of an electrostatic precipitator, the resistivity of the entrained particulate matter from low-sulfur content coal must be reduced. Electrical utilities have long used conditioning agents introduced into the flue gas flow upstream of the electrostatic precipitator to reduce the resistivity of the entrained particles. Various chemicals, such as water, anhydrous ammonia, sulfuric acid, sulfur trioxide, phosphoric acid and various ammonia-bearing solutions have been used as conditioning agents.
Prior art systems used to introduce sulfuric acid into the flue gas have not been economically or technically successful. Substantial quantities of energy have to be transferred to the, sulfuric acid to cause it to vaporize quickly as it is introduced into the flue gas so that it will effectively condition the flue gas for particulate removal. Sulfuric Acid is an aqueous solution. Consequently, sufficient heat energy to vaporize the water of the solution must be applied to effect vaporization thereby increasing the cost of operation. Further, the acid must be brought to disassociation temperature (600.degree.-650.degree. F.) very quickly to prevent metal corrosion.
Thus, it would be a substantial advance in the art to have a system for treating boiler flue gas to improve the removal of particulate matter that utilizes a vaporized solution of sulfuric acid as a conditioning agent that is both effective and economically acceptable. Accordingly, a system for treating boiler flue gas to improve the removal of particulate matter that utilizes vaporized sulfuric acid solution that taps available "waste" energy sources within the system to increase the energy level of the solution to facilitate vaporization in an effective and economically feasible manner would overcome the deficiencies in the prior art.